Power adapters such as the type to which the present invention is directed find application in mobile vehicles which are equipped with significant electrical and electronic equipment. A typical example is a pleasure boat which can be equipped with navigational equipment such as radio and radar, kitchen appliances such as a cooking range and refrigerator, entertainment equipment such as television, and stereo, and other such electrical and electronic equipment. When the craft is in use, the craft engine usually powers a generator which produces output power capable of driving all of those devices. However, when the craft is docked at a marina, it is typical to derive power for the onboard electrical equipment from a stationary source, such as a dockside electrical pedestal at the marina. The marinas are usually equipped with 120 volt power. If all of the appliances on board the craft are also 120 volt devices, and if the power distribution system on the craft is a simple 120 volt system, a docking connector on the craft can be connected to the pedestal at the marina and all of the devices will have power available.
However, if the craft has 240 volt (or 208 volt) equipment, or if the power distribution system on the craft is a 240 volt distribution system, the operator of the craft cannot simply connect a docking power connector on the craft to the pedestal. Marinas have, however, often provided separate 120 volt outlets on the pedestal wired from two phases of a three phase supply so that appropriate voltages are available for powering the equipment on a craft which requires a 240 volt supply. However, those two out-of-phase sources must be connected together in an appropriate manner before they are useful for powering the 240 volt equipment on the craft. Typically, the pedestal simply has the two out-of-phase 120 volt sources brought out to separate receptacles, so that they can be used in the ordinary way for powering 120 volt equipment. If, as is typical, no provision is made for combining the two out-of-phase sources at the pedestal for powering the 240 volt craft, the user is faced with the problem of wiring the two sources together external of the pedestal and bringing the connected sources to the craft. Even if the user had anticipated the problem to the extent of having a harness wired such that input cables for connecting to the pedestal are jumpered together and to an output cable for connection to the craft, the user may expose himself to the danger of shock or injury during the connection process. More particularly, it may not be readily appreciated by the user that when one of the plugs is inserted into a live socket in the pedestal, live voltage can also appear on the other plug; if the user has his body in contact with the electrical prongs of the unconnected plug, he is subjected to the danger of receiving an electrical shock.
As another example, in the case where a marina has 240 volt power but at an insufficient current level for driving all of the appliances on a craft, and the craft is not configured to split the appliances between a pair of power outlets, it is desirable to combine a pair of 240 volt outlets, say each of 50 amp capacity, to provide a 240 volt, 100 amp combined service. As in the prior example, if the sources are not properly wired together, problems can arise both in potential damage to the equipment and harm to the user.
Not all marinas are necessarily wired according to a particular standard, or wired by qualified electricians. If a user attempts to connect to a marina power source which is improperly wired, additional problems can result. In a voltage summing implementation, if the electrical sources from the two selected receptacles are not from different phases, the summed output voltage will not be adequate to drive the equipment on the craft. In a current summing implementation, if the sources from the two selected receptacles are not from the same phase, a phase-to-phase short is possible. Additional problems can result if one of the voltage sources, although of the proper phase, is wired with its polarity reversed. These and other problems can lead to a situation where the user is not adequately advised of the nature of a problem when one exists, and is thus not adequately equipped to deal with an improper connection when jumpering two sources to drive a load. Without adequate information as to what is wrong--the phase, the polarity, a tripped circuit breaker, a potential problem in the equipment onboard, the user may know little more than the fact that certain equipment on the craft is not operating properly. Without substantial experience or additional assistance, he will not be able to readily ascertain whether the problem is in the craft, in the connection, in the pedestal, in the power source back at the marina, etc. The natural response of unconnecting and reconnecting the various plugs in different configurations might lead more directly to additional problems than to a solution.